1. Field of the Invention
The present invention relates to an E. coli-derived upstream regulatory sequence operable in yeast.
2. Description of the Related Art
Recently, information useful for genetic engineering has been rapidly accumulated for yeast as well as E. coli. In addition, yeast is widely used as a host for the production of substances by genetic engineering, because there is much knowhow relating to its fermentation. To express gene coding for a substance to be produced in yeast cells, generally, a powerful promoter of yeast origin is used. The reason is that efficient transcription of a gene is essential for efficient production of a substance. Therefore, promoters of genes for glycolytic enzymes such as phosphoglucokinase (PGK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the like are used. Where a repressible promoter is preferred due to the instability of the heterogeneous gene product in yeast cells or toxicity of the product, a promoter GALl, PHO5, CUP1, ADH2, or the like is used.
It is known that these promoters comprise at least two functionally different regions. One is a region comprising a so-called TATA sequence and a transcription start point (hereinafter designated as "TATA region"), and another is an upstream regulatory sequence (URS) present upstream of the TATA region. Generally, a URS includes an upstream activating sequence (UAS) and an upstream inhibitory sequence (UIS). In yeast, synthesis of a gene product is controlled by controlling the transcription by a combination of these sequences. Moreover, it is known that a URS can function in a combination with a TATA region, different from a combination with a native TATA, and that the functions of UAS and UIS do not depend on the direction relative to the TATA region. Moreover, it is considered that the activity of a promoter reflects the activity of UAS. It is believed that this type of control necessarily applies to expression of a foreign gene.
From the above, it is expected that novel promoters capable of efficient expression of a foreign gene can be developed by a combination of URS's of different genes or a combination of a URS and a TATA region of different genes. According to such a strategy, Bitter et al., Gene, 69, pp 193-207, 1988, reported that they developed a hybrid promoter which can be controlled by galactose and has a transcriptional activity higher than that of a GALl promoter and also developed an efficient expression system for interferon production. In similar attempts, there have been reported a hybrid promoter comprising a combination of a control region of ADH2 and a promoter of GAPDH, which hybrid promoter can be controlled by ethanol and has a transcriptional activity higher than that of an ADH2 promoter (Cousen et al., Gene, 61, pp 265-275, 1987); a hybrid promoter comprising a combination of a control region of a PHO5 and GAPDH promoter, which hybrid promoter can be controlled by a phosphate concentration in a culture medium and has a transcriptional activity higher than that of a PHO 5 promoter (Hinnen et al., Yeast Genetic Engineering, BuHerworth, 1989), and the like. However, although the GAPDH promoter used above contains a UAS of GAPDH, the activities of the above-mentioned hybrid promoters are not greater than those of GAPDH.
As seen from the above, although it is believed that the most powerful promoters in yeast are those of genes for glycolytic enzymes, there have not been reported promoters much more active than native promoters.